docs: Bump version to 1.9.1.

docs/conf.py

@@ -99,7 +99,7 @@ copyright = '2014-2017, Damien P. George, Paul Sokolovsky, and contributors'
 # The short X.Y version.
 version = '1.9'
 # The full version, including alpha/beta/rc tags.
-release = '1.9'
+release = '1.9.1'
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.